AD122-96 MX
Operations Manual
8
Bar-Graph & Display Screen
FINE: OFF 20 METER: -00 0
PEAK/HOLD OFF DISPLAY:3
Bar-Graph settings:
FINE: OFF
sets the bar graph display (LED's) for normal audio monitoring. Setting to
FINE: ON 20
activates the reference meter bridge function, for fine-tuning of signal level to -20dB reference point.
The reference point can be set to a level between -10dB and -20dB by changing the “20” to the desired
reference level. The incoming signal is displayed in 0.2dB increments around the reference point. Fine-
tuning of signal levels may be done via an external volume control or by tuning the GAIN adjustment
pots located on the front panel (the adjustment requires a small screwdriver).
The normal setting, “
METER:-00
” is used for showing peak and peak-hold levels ranging from 0 to -
55dB (from full scale). The display may be extended to indicate lower level activity such as noise and
DC offset.
Meter Setting
Display range
Read Bar-Graph
METER:-00
0dB to -55dB
Read Bar Graph panel indicator
METER:-30
-30dB to -85dB
Add -30dB to panel indicator
METER:-60
-60dB to -115dB
Add -60dB to panel indicator
METER:-90
-90dB to -145dB
Add -90dB to panel indicator
While this feature is useful for determining noise floor of the incoming signal, a few comments are in
order:
1. The Bar Graph displays a sum of AC signal "riding" on a DC offset. Monitoring low-level signals
(such as noise floor) requires prior setting of DC removal at the audio control screen
DC
REMOVAL ON
.
2. Viewing the noise floor takes some getting used to. The display shows a true picture of peak and
peak-hold information; the blinking of LED's is due to low level quantizations. Peak readings are at
about 11dB higher than the rms noise for flat noise spectrum.
3. Measuring the converter noise floor is best done with specialized equipment (such as Lavry
Engineering’s Model LE3000S). To verify the proper converter noise floor via extended metering you
must activate the DC removal (
DC REMOVAL ON
) and connect a low value resistor (0-1k Ohm)
between pins 2 and 3 of the analog input XLR connector. Floating high impedance analog inputs are
susceptible to noise pickup.
Peak/Hold indication:
When set to
ON
, the peak level is held until a front panel switch is depressed. In addition, the “MAX”
LED will turn on and stay on when output data hits the full-scale value. The appropriate 0dB bar-graph
lamp (left or right) will start blinking. The “MAX” and corresponding lamps may be reset by pressing
any of the front panel switches. When PEAK/HOLD is
OFF
, the MAX lamp will flicker when a single
full-scale sample is encountered.
Display contrast: The LCD display may be adjusted from 0 to 7.
The “0” in the upper right corner of the screen is no longer used for setting a parameter in the MX
model. It can be changed to a “1,” but it should normally be set to “0” as the default setting.
